In an emotional speech in a Florentine court on Wednesday, Raffaele Sollecito denied murdering the British student Meredith Kercher six years ago and said he wanted his life back.

Sollecito, 29, said he had spent most of his 20s defending himself from accusations that he had killed Kercher during a sex game. At the end of his 15-minute speech, he appeared to be on the verge on tears. His address followed a morning of complex DNA results being explained to jurors, who often looked confused.

Sollecito said his brief romance with co-defendant Amanda Knox in Perugia was a "little fairytale" that was shattered when the pair were accused of fatally stabbing Kercher in the Italian city. This pushed them into a "nightmare beyond imagination", he said. "I have been described as a ruthless killer but I am nothing of the sort," said Sollecito, during a soft-spoken and occasionally rambling speech.

The trial is the latest in a drawn-out legal process. Knox, 26, and Sollecito were jailed for murder by a Perugian court in 2009 but then freed on appeal in 2011.The latter verdict was overturned by Italy's supreme court this year, sending the case back for a fresh hearing.

While Knox, an American, declined to travel from her home in Seattle to appear in court, Sollecito returned from holiday in the Dominican Republic to go to court, accompanied by his father.

Sollecito told the jury he was proud to come from a "good Italian family", which had taught him strong values and had never had legal problems. "I have always been honest," he said, "but I have been called an assassin."

He claimed he had been a reserved student at Perugia, had not been an "obsessive party-goer" and did not drink. In an apparent reference to photographs of him kissing Knox at the crime scene, he apologised, telling the jury: "I didn't take the situation seriously at the start."

From being one week away from obtaining his degree, he was plunged into six months in isolation followed by a spell in a maximum security prison, he said, adding: "I don't recommend it to anyone in the world. All my life was cancelled."

Speaking without notes, Sollecito condemned what he called his "hallucinatory persecution", complaining that police had believed a footprint found at the house was his before changing their minds eight months later. He said he had never known Rudy Guede, who was also convicted of murder.

There had been speculation that Sollecito was preparing to flee the country after he took a holiday in the Dominican Republic, which does not have an extradition treaty with Italy. But his father said his son's decision to return for the hearing showed he had no plan to escape Italian justice.

Raffaele Sollecito complained that he had been hounded by photographers. "I need to defend myself in the media for the most banal thing," he said. "I have tried to stay out of the limelight. And today I am here in front of you to get to know you and tell you the truth of this matter."

His speech followed an explanation by two Italian police officers of the results of a test on a DNA trace carried out on a knife found at Sollecito's flat, which prosecutors have argued was the murder weapon.

The results allowed police to "support, in an extremely significant manner, the hypothesis that genetic material of Amanda Marie Knox is present" in the trace, the report said.

An earlier police report decided that a separate trace could contain Kercher's DNA, which was used to suggest that the knife was the murder weapon. But that test was challenged as unreliable by a second analysis carried out during the first appeal in 2011.

The latest result has been seized by lawyers representing Knox and Sollecito as proof that the knife was used by Knox and Knox alone in Sollecito's kitchen. "This is just a kitchen knife," said Carlo Dalla Vedova, a lawyer representing the American.

The presiding judge adjourned the trial to 25 November, scheduling further hearings for 26 November, 16 and 17 December, and 9 and 10 January.